Although I do not have a schematic of the AR-88, I just started reading the
thread, so I thought I would jump in more to kick you into changing your
detective methods than to hand you an answer (which I do not know)

If everything was ok before the surgery, and things are now bad, then
something happened during the surgery. That is probably painstakingly
obvious. But, it is important, because it probably rules out changes that
might suddenly have occurred outside of your surgery - such as bad tubes.

So, the question is what happened during the surgery that could cause the
problem. It could be a defective capacitor, or an electrolytic instlled
backwards (especially in negative line). Or, it could be a wire from one of
those components sticking through a terminal and shorting something. Or, it
could be that a resistor got moved and broke in two pieces, but is not
visible. It might be useful to do a resistance check if the manual has one,
or check individual components. Another possibility is, when soldering to a
pot, that the internal connection was broken by the movement of removing and
reconnecting the wires. Same thing on power resistors, especially
adjustable power resistors.

The AVC circuit is usually a long string that can be disconnected in
sections. It sounds like you have been doing that. I think one problem I
had like you are having was when a mica coupling cap in the if stage was
bringing in a small positive leakage into the avc circuit. I kept
addressing the avc circuit, but it was not there at all. Sort of a Trojan
Horse.

The good thing about this is that you will feel very good when you find the
problem. Enjoy the old receiver.

Good luck.

73, Colin K7FM